The present invention relates to a position detecting device which utilizes a liquid having a free surface. More particularly, the invention relates to a position detecting device suitable for an inclination sensor device of a surveying apparatus and which has a compact structure, and to the inclination sensor device of the surveying apparatus using the position detecting device.
JP2000-105119A discloses a position detecting device and a surveying apparatus using the position detecting device, which includes: an emission optical system; a dark field pattern; a liquid; a projection optical system; a first light-condensing element; a second light-condensing element; a first light-receiving sensor; and a second light receiving sensor.
According to the position detecting device and the surveying apparatus of JP2000-105119A, the emission optical system emits a light flux from a light source in parallel, and the dark field pattern includes transit portions, through which the pattern forming light flux from the emission optical system is passed, and arranges the transit portions two-dimensionally in a pattern therein. The liquid, having a free surface, reflects the pattern forming light flux, and the projection optical system projects the pattern forming light flux reflected by the free surface of the liquid. The first light-condensing element structures a part of the projection optical system and condenses the pattern forming light flux in a first direction, and the second light-condensing element also structures a part of the projection optical system and condenses the pattern forming light flux in a second direction which is different from the first direction. The first light-receiving sensor receives projection images of the dark field pattern formed by the pattern forming light flux condensed by the first light-condensing element, and the second light-receiving sensor receives the projection images of the dark field pattern formed by the pattern forming light flux condensed by the second light-condensing element.
Thereby, the position detecting device and the surveying apparatus of JP2000-105119A detects positions of the projection images of an X-direction and positions of the projection images of a Y-direction based on a light-receiving signal of the first light-receiving sensor and a light-receiving signal of the second light-receiving sensor, so as to obtain movement amounts of the projection images from a reference position. The position detecting device and the surveying apparatus of JP2000-105119A also converts the obtained movement amounts of the projection images to an angle of inclination.
The JP2000-105119A further discloses an inclination sensor device of the surveying apparatus utilizing such a position detecting device.
According to the position detecting device and the inclination sensor device of the surveying apparatus utilizing the same of the JP2000-105119A, however, because the pattern forming light flux, reflected from the free surface of the liquid, is made to condense in the directions different from each other by utilizing the first light-condensing element and a cylindrical lens as the second light-condensing element each structuring the part of the projection optical system, and then the condensed light fluxes are received by the first light-receiving sensor and the second light-receiving sensor, respectively, there are problems that the structure of the projection optical system is complicated, and the position detecting device and the inclination sensor device are difficult to achieve compactification.